a) Field of the Invention
The invention is directed to a vacuum valve. The invention relates especially to a vacuum valve comprising a valve body with a valve opening having an axis; a closing member which is displaceable between an open position of the valve and a closed position of the valve in a closing direction extending at an angle to the axis of the valve opening; a sealing surface which surrounds the valve opening and which has at least two main portions which are arranged so as to be offset relative to one another in direction of the axis of the valve opening, are connected with one another by connection portions, and whose imaginary generating lines have at least a portion or a tangent extending substantially vertical to the closing direction; a circumferentially closed seal which is arranged at the closing member and which has two main portions corresponding to the main portions of the sealing surface and connection portions which connect these two main portions of the seal, which seal can be placed against the sealing surface by means of a displacement of the closing member in the closed position of the valve.
b) Description of the Related Art
Slide valves with a valve housing forming the valve body are known. Its valve opening is surrounded by a sealing surface lying in a plane arranged at right angles to the axis of the valve opening. The valve opening is displaceable by a plate-shaped closing member to which a ring seal is secured, this ring seal being arranged in a plane parallel to the plane of the sealing surface. In order to prevent transverse forces acting on the seal, the closing movement is carried out in two steps. First, the plate-shaped closing member is moved into a position which is located opposite the valve opening but is raised from the sealing surface. Subsequently, a portion of the multiple-part closing member carrying the seal is displaced in the direction of the valve opening until the seal contacts the sealing surface. For this purpose, spreading devices, for example, are provided for spreading apart the closing member which is formed of multiple parts. Vacuum valves of this type which have a relatively complicated construction and in which a relatively large quantity of particles is released into the vacuum in an unwanted manner during the closing process, particularly by the movement between the parts of the closing member, are known, for example, from U.S. Pat. No. 4,560,141 or U.S. Pat. No. 4,291,861.
Vacuum valves of the type mentioned in the beginning are known from U.S. Pat. No. 4,881,717, U.S. Pat. No. 4,809,950, and U.S. Pat. No. 5,909,867. The contents of these patents are hereby adopted through reference. The valves taught in these patents have a simple construction, can be opened and closed quickly, wherein transverse forces are prevented from acting upon the seal, and release substantially fewer particles during the closing and opening process compared to the valves described above.
When a differential pressure occurs between the areas on either side of the closing member when the vacuum valve is closed, considerable forces result which cause a certain lateral displacement of the closing member, i.e., in direction of the axis of the valve opening. This lateral displacement is limited in direction of the valve opening by the valve body. A differential pressure strip which is also shown in FIGS. 4 and 5 of U.S. Pat. No. 5,909,867 can be provided for limiting this displacement in the opposite direction. When the closing member strikes the differential pressure strip or the valve body due to a displacement resulting from a differential pressure, there is metal-to-metal contact so that particles are released into the vacuum in an unwanted manner. For this reason, it has already been suggested that the differential pressure strip be provided with a rubber coating. This increases the overall cost of the valve. In FIG. 5 of U.S. Pat. No. 4,809,950 and in FIG. 8 of U.S. Pat. No. 4,881,717, protective edges are provided at the closing member which, in the closed condition, engage in grooves that are arranged in the sealing surface. The protective edges are intended to shield the seal from a flow penetrating the valve opening when the closing member moves in, so as to protect the seal.
An important object of the invention is to provide a vacuum valve of the type mentioned in the beginning in which a support is provided in a simple manner against a differential pressure acting on the closing member in the closed state of the valve, and in which as few particles as possible are released into the vacuum. Another object of the invention is to provide a vacuum valve of the type mentioned in the beginning which achieves improved protection of the seal relative to influences caused by processes carried out in the vacuum chamber in which the vacuum valve is used, for example, protection against process gases used in the vacuum chamber or plasma generated in the vacuum chamber.
A vacuum valve, according to the invention, comprises a valve body with a valve opening having an axis; a closing member which is displaceable between an open position of the valve and a closed position of the valve in a closing direction extending at an angle to the axis of the valve opening; a sealing surface which surrounds the valve opening and which has at least two main portions which are arranged so as to be offset relative to one another in direction of the axis of the valve opening, are connected with one another by connection portions, and whose imaginary generating lines have at least a portion or a tangent extending substantially vertical to the closing direction; a circumferentially closed seal which is arranged at the closing member and which has two main portions corresponding to the main portions of the sealing surface and connection portions which connect these two main portions of the seal, which seal can be placed against the sealing surface by means of a displacement of the closing member in the closed position of the valve, wherein at least one of the main portions of the seal has a depression or recess at least along a portion of its length, considered in cross section, on its side facing the sealing surface, and is arranged in a recess of the closing member whose side flanks support the seal laterally, and the corresponding portion of the sealing surface is arranged on a protuberance of the valve body or is provided with a protuberance, which protuberance can be inserted in the recess of the seal when the valve is closed.
Improved support is achieved in case of differential pressure by means of the construction, according to the invention, of the seal and of the area of the closing member receiving the seal and of the area of the valve body having the sealing surface, wherein metal-to-metal contact between the closing member and the valve body can be prevented. Further, the portion of the seal arranged in the recess of the closing member is better protected against process gases used in the vacuum chamber and against plasma generated in the vacuum chamber.
In an advantageous embodiment example of the invention, the seal is arranged in a recess in the closing member at least along the greater part of the longitudinal extension of the two main portions and is provided with a recess which receives the sealing surface arranged on a protuberance of the valve body or which receives a protuberance of the sealing surface. In a particularly advantageous embodiment form of the invention, this is carried out over the entire longitudinal extension of the seal or sealing surface. Penetration of aggressive gas particles from the process area to the seal is accordingly slowed down or hindered and the area attacked by the process gases at the seal is minimized. It has also been observed that process gases act more aggressively on areas of the seal subjected to high mechanical stresses than on areas that are less mechanically deformed. According to the invention, however, the highly stressed areas of the seal can be extensively shielded from the influencing process gases.
In order to further slow down or hinder penetration of aggressive gas particles to the seal, at least one groove can be provided in the closing member on at least one side of the seal, which groove extends along the entire length of the seal laterally alongside the seal, and a projection which is provided at the valve body and extends laterally alongside the sealing surface around the valve opening projects into the groove. This effect is further enhanced when two or more such grooves and projections are provided.